HOW DO GENES INFLUENCE MARIJUANA USE - THE ROLE OF SUBJECTIVE EFFECTS

This study investigated determinants of the subjective effects of mari juana and the relationship of subjective effects to marijuana use. Sub jects were 8169 twins drawn from the Vietnam Era Twin Registry. Subjec ts who used marijuana more than five times (n = 2513) reported whether they experienced each of 23 subjective reactions. Factor analysis ide ntified a positive (pleasant) reaction factor and a negative (unpleasa nt) reaction factor. Both factors were related to duration and frequen cy of use. Pairs in which both members used marijuana more than five t imes (MZ = 352 pairs; DZ = 255 pairs) were examined to assess determin ants of subjective effects. Approximately one-quarter of the variance in each factor was determined by additive genetic influences; the rema ining variance was determined by environmental factors that are not sh ared by members of a twin pair. The shared or family environment had n o detectable influence on either subjective reaction factor.